JP5295397B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an image forming equipment, especially Rezabi scans the image bearing member such as a photosensitive drum - related beam on / off control.

  In an electrophotographic image forming apparatus, generally, a laser beam emitted from a semiconductor laser is turned on and off, and this laser beam is scanned with a rotating polygon mirror (polygon mirror) and irradiated onto a photosensitive member. Then, latent image formation is performed.

  In such an image forming apparatus, an image clock having a constant frequency is usually used for on / off control of laser light. The reason is that if the frequency of the image clock is not constant, the on / off timing of the laser beam deviates from the normal timing, thereby causing the dot formation position of the electrostatic latent image formed on the photoreceptor to deviate slightly. As a result, image distortion, color shift, and color unevenness occur.

  In addition, an f-θ lens is provided between the polygon mirror and the photosensitive member. The f-θ lens has optical characteristics such as a laser beam condensing function and a distortion correction function that guarantees the temporal linearity of scanning, and thus the laser beam that has passed through the f-θ lens. Are combined and scanned on the photosensitive member at a constant speed in a predetermined direction.

  However, due to the deviation of the characteristics of the f-θ lens, the laser light irradiated onto the photosensitive member may be deviated from an ideal image forming position. Therefore, a frequency modulation technique is used in which the reference image clock is modulated to finely adjust the on / off timing of the laser beam and correct the position of the dot formed on the photosensitive member (for example, Patent Document 1). reference).

  However, when the image clock is always constant, radiation noise is generated in a transmission path for transmitting an on / off signal for controlling on / off of laser light from the generation circuit to the laser driving circuit. In many cases, the radiation noise level exceeds a value defined in international radiation noise standards.

  In addition, when using a frequency modulation technique, the radiation noise level is reduced, but when using an f-θ lens having a characteristic that does not require frequency modulation, the frequency of the image clock becomes constant. The radiated noise level becomes more severe.

  In a tandem color image forming apparatus in which color misregistration in the main scanning direction is a problem, frequency modulation is often used to correct the characteristics of the f-θ lens. However, frequency modulation is rarely performed in a one-drum color image forming apparatus that does not need to worry about color misregistration in the main scanning direction and a monochrome image forming apparatus that does not require consideration for color misregistration. Even in that case, the radiation noise level often exceeds the value of the international radiation noise standard, which is a problem.

  As a technique for reducing the noise level due to the image clock, a technique has been proposed in which the peak level of radiation noise in a specific frequency band is reduced by changing the frequency of the image clock by a certain amount of fluctuation ( For example, see Patent Document 2).

Japanese Patent Laid-Open No. 2-282863 JP 2004-268504 A

  FIG. 5A is an explanatory diagram when image clock modulation (frequency modulation) is applied to a multi-beam type laser scanner unit. Normally, in the case of the multi-beam method, as shown in FIG. 5B, the laser chip is tilted and adjusted so that the spot interval of the laser beam on the drum surface becomes a sub-scanning pitch determined by the resolution.

  At this time, since the relative positions of the A laser and the B laser in the main scanning direction are not the same, the writing is started with the A laser and the B laser being shifted by the shift in the main scanning direction. In this case, for example, when modulation of the A laser and the B laser is started after the lapse of the same time on the basis of the BD signal, an ideal position shift amount caused by frequency modulation is caused by the A laser and the B laser as shown in FIG. It will be different. For this reason, the dot position shift occurs between the A laser and the B laser, which adversely affects the image.

  Also, when the frequency modulation period and amplitude are modulated differently for each laser depending on the image position, the amount of deviation from the ideal position is also different for each laser, which causes dot position deviation.

  Also in the case of the tandem method, as shown in FIG. 13, color misregistration occurs for the same reason as described above, and the image is adversely affected.

Accordingly, an object of the present invention is to provide an image forming equipment obtained image without color shift due to frequency modulation.

To achieve the above object, an image forming apparatus according to the present invention, an image based on image data to form an electrostatic latent image on the photosensitive member to rotate, to form an image by developing the electrostatic latent image in forming apparatus, a first light emitting point which emits the first light beam, and a second emission point emitting a second light beam, the first light emitting point in the rotation axis direction of the photosensitive member The second light beam emitted from the second light-emitting point and the second light beam emitted from the second light-emitting point are imaged at different positions with respect to the first light-emitting point. A light source for forming the electrostatic latent image on the photosensitive member by exposing the photosensitive member with the first light beam and the second light beam, and the first light beam. and said second light beam scans on the photosensitive member And deflecting means for deflecting the first light beam and said second light beam so that, to generate a first image clock signal for periodically varying the frequency depending on time, according to the time elapsed Generating means for generating a second image clock signal, the frequency of which fluctuates in the same cycle as the first image clock signal, the phase of which is adjusted with respect to the phase of the first image clock signal ;
Based on the first image clock signal and the image data, a first drive signal for emitting the first light beam from the first light emitting point is generated, and the second image clock signal and Based on the image data, a second drive signal for emitting the second light beam from the second light emitting point is generated, and based on the first drive signal and the second drive signal characterized in that it comprises a driving means for driving the light source.

  According to the present invention, when noise reduction is performed by modulating the frequency of an image clock with a predetermined fluctuation amount, an image free from color shift due to frequency modulation can be obtained.

1 is a diagram schematically showing a configuration of an exposure unit of an image forming apparatus according to a first embodiment of the present invention. It is a block diagram of the frequency modulation apparatus which concerns on the 1st Embodiment of this invention used for drive control of the laser light source in FIG. It is a block diagram which shows the structure of the frequency modulation parameter in FIG. It is a block diagram which shows the structure of the light emission signal production | generation means in FIG. FIG. 3 is a diagram illustrating a relationship between a frequency of an image clock generated by the frequency modulation device of FIG. 2 and a main scanning position (No. 1). FIG. 3 is a diagram showing a relationship between the frequency of an image clock generated by the frequency modulation device of FIG. 2 and a main scanning position (No. 2). FIG. 3 is an explanatory diagram in the case of controlling the modulation timing from the basic period of the image clock by modulating the period of the image clock outside the image area before the start of image writing in the frequency modulation apparatus of FIG. 2. In the frequency modulation apparatus of FIG. 2, it is explanatory drawing when not generating an image clock at the timing outside an image area until it reaches an image area. It is a figure which shows typically the structure of the exposure unit of the image forming apparatus which concerns on the 2nd Embodiment of this invention. FIG. 10 is a block diagram of a frequency modulation apparatus according to a second embodiment of the present invention used for driving control of the laser light source in FIG. 9. It is a block diagram which shows the structure of the frequency modulation parameter in FIG. It is a block diagram which shows the structure of the light emission signal production | generation means in FIG. FIG. 11 is an explanatory diagram showing the relationship between the frequency of an image clock generated by the frequency modulation device of FIG. 10 and the main scanning position (No. 1). FIG. 11 is an explanatory diagram illustrating a relationship between the frequency of an image clock generated by the frequency modulation device of FIG. 10 and a main scanning position (part 2).

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram schematically showing a configuration of an exposure unit of the image forming apparatus according to the first embodiment of the present invention.

  The electrophotographic image forming apparatus, as shown in FIG. 1, forms a latent image corresponding to input image data on the photosensitive drum 15 (on the photosensitive member). 15 is provided with an exposure unit for irradiating a laser beam to 15.

  The exposure unit includes a laser light source 1 having two light emitting points (not shown) that emit diffuse laser light, an A laser (first light emitting point) and a B laser (second light emitting point). Laser light emitted (emitted) from the laser light source 1 is converted into parallel laser light L1 and L2 via the collimator lens 13, and the laser light L1 and L2 (that is, the first light beam and the second light beam). ) Is irradiated to the polygon mirror-2 being rotated by the scanner motor 3. The laser beams L1 and L2 irradiated to the polygon mirror-2 are deflected (reflected) by the polygon mirror-2 and reach the f-θ lens 14.

  The laser beams L1 and L2 that have passed through the f-θ lens 14 are combined and scanned on the photosensitive drum 15 at a constant speed in the main scanning direction, and a latent image (on the photosensitive drum 15 is scanned by this laser beam, that is, a scanning operation). 16 (also called an electrostatic latent image) is formed. That is, the laser beam L1 exposes the first exposure position of the photosensitive drum 15, and the laser beam L2 exposes the second exposure position adjacent to the first exposure position in the rotation direction of the photosensitive drum 15. The start of the laser beam scanning operation is detected by a beam detect sensor (hereinafter referred to as a BD sensor) 17. The electrostatic latent image on the photosensitive drum 15 is developed by a developing device and visualized.

  The laser light source 1 is forcibly turned on at the time corresponding to the start of scanning of the laser beam on the photosensitive drum 15. The BD sensor 17 detects the laser beam L1 reflected and input by the polygon mirror-2 during the forced lighting period of the laser light source 1, and a beam detect signal (hereinafter referred to as a reference signal for image formation writing timing for each main scan). , A BD signal) as a detection result.

  Next, the frequency modulation configuration of the image clock used for driving control of the laser light source 1 will be described with reference to FIGS.

  FIG. 2 is a block diagram of the frequency modulation apparatus according to the first embodiment of the present invention used for drive control of the laser light source in FIG.

  In the image clock frequency modulation device 114 used for driving control of the laser light source 1, as shown in FIG. 2, a reference clock generating means 104 for generating a reference clock (reference clock signal) 21, a memory 113, and an image decoder. -Data generation means 115 and light emission signal generation means 101 are provided.

  The memory 113 stores a frequency modulation setting parameter 106, and the frequency modulation setting parameter 106 includes various setting values required for the image clock signal modulation operation of the frequency modulation device 114.

  FIG. 3 is a block diagram showing the configuration of the frequency modulation parameter in FIG.

  As shown in FIG. 3, the image clock basic period setting value 107, which is a setting value corresponding to the basic period of the image clock generally determined by the drum surface scanning speed and resolution of the laser, is set for each of the A laser and the B laser. Remember against.

  Further, an image clock modulation amount setting value 108, which is a setting value corresponding to the maximum amount (period fluctuation width) to be expanded / contracted from the basic cycle of the image clock, is stored for each of the A laser and the B laser.

  Also, an image clock modulation period setting value 109 is set for each of the A laser and the B laser, which is modulated from the basic period, takes the maximum and minimum periods, and sets how many pixels are required to return to the basic period. .

  In addition, after inputting the BD signal, an image clock modulation start timing setting value 110 for setting a timing for starting modulation in accordance with an image clock modulation amount and an image clock modulation period is stored for each of the A laser and the B laser.

  These various set values are transferred to the light emission signal generation means 101. As shown in FIG. 4, the image data generating means 115 generates image data 22 that is a signal for controlling the lighting of the laser light source 1 to form an image. One line of image data 22 corresponding to each laser light source 1 is sent to each light emission signal generating means 101. This image data 22 is stored in the shift register 116 in the light emission signal generating means 101.

  The light emission signal generation unit 101 includes a segment division unit 102 and an image clock generation unit 103. The segment dividing unit 102 divides one line scanned in the main scanning direction into a plurality of segments configured by the number of pixels determined by the image clock modulation period setting value 109.

  The image clock generation unit 103 generates an image clock corresponding to each divided segment based on the reference clock (reference clock signal) 21 generated by the reference clock generation unit 104. Specifically, the image clock generation unit 103 generates an image clock having the image clock basic period setting value 107 as a basic period and whose period is modulated according to the image clock modulation amount setting value 108.

  Modulation is started at the timing set by the image clock modulation start timing setting value 110, and the modulated image clock is output to the shift register 116. The shift register 116 receives the image clock and sequentially outputs a light emission signal to the laser driving circuit 112 according to the stored image data. The laser drive circuit 112 outputs a drive signal for controlling the light emission of each laser in accordance with the input light emission signal 18 (that is, outputs a first drive signal and a second drive signal). 2 and 4, reference numeral 29 denotes a BD signal.

  Next, image clock modulation with the above frequency modulation configuration will be described with reference to FIGS. 5 and 6 are diagrams showing the relationship between the frequency of the image clock generated by the frequency modulation device of FIG. 2 and the main scanning position. FIG. 5A is a diagram when the modulation period, modulation amount, and modulation start timing of the A laser and the B laser are separately modulated.

  (A) -1 indicates a BD signal, and indicates the timing until the BD signal is detected after the BD signal is detected, that is, the laser scans once on the drum surface. (A) -2 is a figure which shows the frequency change of the image clock of A laser in 1 scan. The vertical axis represents the frequency of the image clock, and the horizontal axis represents the count number of the image clock.

  In this figure, after BD detection, counting is performed at the same frequency up to 500 counts, and from the 501st count, it is counted as 100 counts per cycle while changing the frequency with a constant fluctuation amount of ± 2%. ing. The image writing timing is from the 501st count.

  (A) -3 is a figure which shows the shift | offset | difference amount from the ideal position on the drum surface of the dot at the time of making a laser drive with the image clock frequency of (a) -2. The vertical axis indicates the amount of deviation from the ideal position, and the horizontal axis indicates the main scanning position on the drum surface. Usually, the exposure unit of the image forming apparatus is designed with an optical system so that laser light scans at a constant speed on the drum surface.

  This embodiment is also based on the premise that it is designed to perform constant speed scanning. In this case, when the frequency of the image clock is constant, the interval between dots is constant. Since the image data for driving the laser is generated with the same interval between dots, if the frequency of the image clock is changed as in the present embodiment, the dot is shifted to a location shifted from the ideal position. Is formed.

  The amount of deviation is indicated by the amount of deviation from the ideal position (a) -3. Since the dot interval decreases as the frequency increases, the amount of deviation from the ideal position shifts to the minus side. On the contrary, since the dot interval becomes wider as the frequency becomes lower, the deviation amount from the ideal position is shifted to the plus side. (A) -2 and (a) -3 have such a relationship.

  (A) -4 is a figure which shows the mode of the frequency change of the image clock of B laser similarly to (a) -2. The start timing of the frequency change is after 501 clocks as in the case of the A laser, but the leading edge of the image is from the 551th count. The frequency modulation amount is ± 1% and the modulation period is 90 counts, which is different from the modulation amount and modulation period of the A laser. (A) -5 is a figure which shows the deviation | shift amount from the ideal position on the drum surface of the dot formed by B laser similarly to (a) -3.

  FIG.5 (b) is the figure which accumulated Fig.5 (a) -3 and (a) -5. FIG. 5C is a diagram showing the positional relationship between the emission points of the A laser and the B laser. As shown in this figure, in the case of a system using a multi-beam, the sub-scanning interval on the drum surface of the A laser beam and the B laser beam is adjusted by tilting the chip to adjust the interval according to the resolution. . For this reason, the relative positions of the A laser and the B laser in the main scanning direction vary depending on the tilt angle.

  By changing the image writing start timing in accordance with the deviation of the main scanning position as shown in FIGS. 5 (a) -2 and (a) -4, an image drawn with the A laser and an image drawn with the B laser Are written on the drum surface at the same position.

  However, when the modulation amount, the modulation period, and the image clock modulation timing are different between the A laser and the B laser as shown in FIGS. 5 (a) -2 and (a) -4, depending on the image height as shown in FIG. 5 (b). The amount of deviation from the ideal position varies between beams. As a result, the main scanning position shift occurs, and the image is adversely affected, for example, when the vertical line is written, the line becomes jagged as shown in FIG.

  FIG. 6 is an explanatory diagram when the image clock modulation start timing is changed in accordance with the image writing start timing in the frequency modulation apparatus of FIG.

  In FIG. 6A, the modulation start timing of the modulation timing of the B laser image clock is delayed by the same number of clocks as the delay clock of the image writing timing. The modulation period and modulation amount of the image clock are the same for both the A laser and the B laser as 100 clock periods, ± 1% (the image clock of the A laser is called the first image clock signal, and the image clock of the B laser is 2 is called image clock signal). Further, the difference in period from the adjacent pixel is 1% × 2 ÷ 25 clock = 0.08%. In this case, as shown in FIG. 6B, the deviation amounts from the ideal positions of the A laser and the B laser coincide with each other at each image height.

  FIG. 6C is a diagram of an ideal position and a dot position when the shift amount is 0, and FIG. 6D is a diagram when the shift amount is 1%. In the case of FIG. 6D, both the A laser and the B laser are deviated from the ideal position. However, since the deviation amount is the same for each image height in the main scanning direction on the drum surface, the dot position deviation between the lasers is Does not occur.

  In the case of the present embodiment, the human recognition level is ± 1.02 pixels at the position where the deviation amount from the ideal position is maximum, and the difference in dot size between adjacent pixels is as small as 0.0008 pixels. However, it is a level at which it can hardly be recognized that the position is deviated from the ideal position.

  FIG. 7 is an explanatory diagram in the case of controlling the modulation timing from the basic period of the image clock by modulating the period of the image clock outside the image area before the start of image writing in the frequency modulation apparatus of FIG. Based on the BD signal, the frequency modulator is an image forming period in which the first light beam or the second light beam is emitted to form an electrostatic latent image on the photosensitive member, and other periods. A non-image forming period is determined.

  (A) -1 indicates the BD signal 29, and shows the timing until the BD signal 29 is detected after the BD signal 29 is detected, that is, the laser scans once on the drum surface. . (A) -2 is a figure which shows the frequency change of the image clock of A laser in 1 scan. The vertical axis represents the frequency of the image clock, and the horizontal axis represents the count number of the image clock. In this figure, after BD detection, counting is performed at the same frequency up to 500 counts, and from the 501st count, it is counted as 100 counts per cycle while changing the frequency with a constant fluctuation amount of ± 2%. ing. The image writing timing is from the 501st count.

  (A) -3 is a figure which shows the shift | offset | difference amount from the ideal position on the drum surface of the dot at the time of making a laser drive with the image clock frequency of (a) -2. The vertical axis indicates the amount of deviation from the ideal position, and the horizontal axis indicates the main scanning position on the drum surface. (A) -4 is a figure which shows the mode of the frequency change of the image clock of B laser similarly to (a) -2. The start timing of the frequency change is after 501 clocks as in the case of the A laser, but the clock frequency up to the 500th clock is set low and the time is 550 clocks when the frequency is not changed. It is set as follows. For this reason, the timing of image writing is the same as that of the B laser in FIG. 6, so writing starts from the same position as the B laser in FIG. 6. According to this method, since the image clock period outside the image area is modulated, the effect of noise reduction is further enhanced.

  FIG. 8 is an explanatory diagram in the case where the image clock is not generated at a timing outside the image area until the frequency modulation apparatus of FIG. 2 reaches the image area. In this case, noise is not generated during the time when the clock is not generated, so that the effect of noise reduction is further enhanced.

  In the present embodiment, the image clock modulation period is set to the same period for each image height during one scan. However, if the period between each station is the same for each image height, the period during one scan is set. May not be constant.

  As described above, according to the present embodiment, it is possible to provide an image in which the peak position of noise caused by the image clock is reduced and the dot position deviation between multi-beams due to frequency modulation does not occur.

  FIG. 9 is a diagram schematically showing a configuration of an exposure unit of the image forming apparatus according to the second embodiment of the present invention. In this embodiment, an exposure unit of a tandem image forming apparatus is shown.

  As shown in FIG. 9, the image forming apparatus includes YCMK and four station image forming units (exposure unit and photosensitive drum 15). The configuration of each station is the same as in FIG.

  Next, a frequency modulation configuration of an image clock used for driving control of the laser light source 1 will be described with reference to FIGS. FIG. 10 is a block diagram of a frequency modulation apparatus according to the second embodiment of the present invention used for drive control of the laser light source in FIG.

  In the image clock frequency modulation device 114 used for driving control of the laser light source 1, as shown in FIG. 10, a reference clock generating means 104 for generating the reference clock 21, a memory 113, an image data generating means 115, A light emission signal generation means 101 is provided.

  The memory 113 stores a frequency modulation setting parameter 106, and the frequency modulation setting parameter 106 includes various setting values required for the image clock signal modulation operation of the frequency modulation device 114.

  FIG. 11 is a block diagram showing the configuration of the frequency modulation parameter in FIG.

  As shown in FIG. 11, the image clock basic period setting value 107, which is a setting value corresponding to the basic period of the image clock generally determined by the laser drum surface scanning speed and resolution, is set to Y, M, C, K. Remember for each of the lasers.

  Also, an image clock modulation amount setting value 108, which is a setting value corresponding to the maximum amount of expansion / contraction from the basic period of the image clock (corresponding to the fluctuation amount of the image clock), is stored for each of the Y, M, C, and K lasers. doing. Also, an image clock modulation period setting value 109 is set for each of the Y, M, C, and K lasers, which is modulated from the basic period, takes the maximum and minimum periods, and sets how many pixels are required to return to the basic period. doing.

  Further, after inputting the BD signal, the image clock modulation start timing setting value 110 for setting the timing for starting the modulation according to the image clock modulation amount and the image clock modulation period is stored for each of the Y, M, C, and K lasers. Yes.

  These various set values are transferred to the light emission signal generation means 101. As shown in FIG. 10, the image data generating means 115 generates image data 22 that is a signal for forming an image by controlling lighting of the lasers of the Y, M, C, and K stations. Image data 22 corresponding to each laser light source 1 is sent to each light emission signal generating means 101. This image data 22 is stored in the shift register 116 in the light emission signal generating means 101.

  The light emission signal generation unit 101 includes a segment division unit 102 and an image clock generation unit 103 as shown in FIG. The segment dividing unit 102 divides one line scanned in the main scanning direction into a plurality of segments configured by the number of pixels determined by the image clock cycle setting value 109.

  The image clock generation unit 103 generates an image clock corresponding to each divided segment based on the reference clock 21 generated by the reference clock generation unit 104. Specifically, an image clock whose frequency is modulated according to the image clock modulation amount setting value 108 is generated using the image clock basic cycle setting value 107 as a basic cycle.

  Modulation is started at the timing set by the image clock modulation start timing setting value 110, and the modulated image clock is output to the shift register 116. The shift register 116 receives the image clock and sequentially outputs a light emission signal to the laser driving circuit 112 according to the stored image data. The laser drive circuit 112 controls the emission of each laser according to the input emission signal.

  Next, image clock modulation with the above frequency modulation configuration will be described with reference to FIGS. 13 and 14 are explanatory diagrams showing the relationship between the frequency of the image clock generated by the frequency modulation device of FIG. 10 and the main scanning position. FIG. 13A is a diagram when the modulation period, modulation amount, and modulation start timing of the Y station laser light source and the M station laser light source are separately controlled.

  (A) -1 indicates the BD signal 29, and shows the timing until the BD signal 19 is detected after the BD signal 29 is detected, that is, the laser scans once on the drum surface. . (A) -2 is a figure which shows the frequency change of the image clock of Y laser in 1 scan. The vertical axis represents the frequency of the image clock, and the horizontal axis represents the count number of the image clock. In this figure, after detecting the BD signal, counting is performed at the same frequency up to 500 counts, and from the 501st count, it is counted as 1 cycle 100 counts while changing the frequency with a constant fluctuation amount of ± 2%. Show. The image writing timing is from the 501st count.

  (A) -3 is a figure which shows the shift | offset | difference amount from the ideal position on the drum surface of the dot at the time of making a laser drive with the image clock frequency of (a) -2. The vertical axis indicates the amount of deviation from the ideal position, and the horizontal axis indicates the main scanning position on the drum surface. Usually, the exposure unit of the image forming apparatus is designed with an optical system so that laser light scans at a constant speed on the drum surface. This embodiment is also based on the premise that it is designed to perform constant speed scanning.

  In this case, when the frequency of the image clock is constant, the interval between dots is constant. Since the image data for driving the laser is generated with the same interval between dots, if the frequency of the image clock is changed as in the present embodiment, the dot is shifted to a location shifted from the ideal position. Is formed.

  The amount of deviation is indicated by the amount of deviation from the ideal position (a) -3. Since the dot interval decreases as the frequency increases, the amount of deviation from the ideal position shifts to the minus side. On the contrary, since the dot interval becomes wider as the frequency becomes lower, the deviation amount from the ideal position is shifted to the plus side. (A) -2 and (a) -3 have such a relationship.

  (A) -4 shows the BD signal 29, and shows the timing until the BD signal 29 is detected after the detection of the BD signal 29, that is, the laser scans once on the drum surface. . (A) -5 is a figure which shows the mode of the frequency change of the image clock of M laser similarly to (a) -2. Like the Y laser, the start timing of the frequency change is after 501 clocks, but the leading edge of the image is from the 551th count. The frequency modulation amount is ± 1% and the modulation cycle is 90 counts, which is different from the Y laser modulation amount and the modulation cycle. (A) -6 is a figure which shows the deviation | shift amount from the ideal position on the drum surface of the dot formed by B laser similarly to (a) -3.

  FIG.13 (b) is the figure which superimposed Fig.13 (a) -3 and (a) -6. In the case of a tandem type system, the timing from the detection of the BD signal to the start of writing varies depending on the unit due to an installation error of the exposure unit, an installation error of the BD sensor 17, and the like. Therefore, by changing the image writing start timing as shown in FIGS. 13 (a) -2 and (a) -5, the Y station image and the M station image overlap on the drum surface.

  However, when the modulation amount, the modulation period, and the image clock modulation timing are different between the Y station laser and the M station laser as shown in FIGS. 13 (a) -2 and (a) -5, FIG. 13 (b). As described above, the amount of deviation from the ideal position differs between stations depending on the image height. As a result, color misregistration is adversely affected.

  FIG. 14 is a diagram in the case where the image clock modulation start timing is changed in accordance with the image writing start timing, and the modulation period and the modulation amount are aligned between the stations.

  In FIG. 14A, the modulation is started by delaying the image clock modulation start timing of the M station laser by the same number of clocks as the delay clock of the image writing timing. The modulation cycle and modulation amount of the image clock are the same as 100 clock cycles and ± 1% for both the Y station laser and the M station laser.

  Further, the difference in period from the adjacent pixel is 1% × 2 ÷ 25 clock = 0.08%. In this case, as shown in FIG. 14B, the amount of deviation from the ideal position of the Y station image and the M station image is the same at each image height. In this case, as shown in FIG. 14, the amount of deviation from the ideal position of the image of each station is the same at each image height in the main scanning direction on the drum surface. do not do.

  Controlling the writing timing by image clock modulation before the image area is more effective for noise reduction. Further, if the image clock is not output at the timing corresponding to the outside of the image area, the noise reduction effect is further enhanced.

  As described above, in the embodiment of the present invention, the first image clock signal and the second image clock signal whose frequency varies with time regardless of the magnification of the image are generated according to the reference clock signal. Is done. Then, the first exposure position on the photosensitive drum is exposed by the first light beam, and the second exposure position adjacent to the first exposure position in the rotation direction of the photosensitive drum is exposed by the second light beam. The first drive signal and the second drive signal are respectively generated by the first image clock signal and the second image clock signal having the same frequency.

  Further, as is apparent from the above description, the first light emission point and the second light emission point in the light source are simultaneously deflected in the scanning direction in which the first light beam and the second light beam scan the photosensitive drum. The first light beam and the second light beam are arranged to expose different positions. Furthermore, when the first light beam is detected, the first frequency of the first image clock signal generated based on the reference clock signal is the same as the initial frequency of the second image clock signal. Image clock signal and the second image clock signal are generated. Then, the generation timings of the first image clock signal and the second image clock signal are made different according to the difference in exposure position between the first light beam and the second light beam in the scanning direction. In addition, the first image clock signal and the second image clock signal are changed at a predetermined period from the initial frequency of the first image clock signal and the second image clock signal.

  As mentioned above, although this invention was demonstrated based on embodiment, this invention is not limited to these embodiment, Various forms of the range which does not deviate from the summary of this invention are also contained in this invention. .

  The present invention can also be realized by executing the following processing. That is, software (program) for realizing the functions of the above-described embodiments is supplied to a system or apparatus via a network or various recording media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program. It is a process to be executed.

101 Light emission signal generating means (modulated image clock generating means)
DESCRIPTION OF SYMBOLS 102 Segment division means 103 Image clock generation means 104 Reference clock generation means 112 Laser drive circuit 113 Memory 114 Frequency modulation apparatus 115 Image data generation means 116 Shift register

Claims (12)

In an image forming apparatus that forms an electrostatic latent image on a rotating photoreceptor based on image data, and forms the image by developing the electrostatic latent image.
A first light emitting point that emits the first light beam and a second light emitting point that emits the second light beam are emitted from the first light emitting point in the rotation axis direction of the photoconductor. The second light emitting point is located with respect to the first light emitting point so that the first light beam and the second light beam emitted from the second light emitting point are imaged at different positions. A light source disposed and forming the electrostatic latent image on the photoreceptor by exposing the photoreceptor with the first light beam and the second light beam;
Deflecting means for deflecting the first light beam and the second light beam so that the first light beam and the second light beam scan on the photoreceptor;
A first image clock signal having a frequency that periodically varies with the passage of time is generated, and the frequency varies with the same cycle as the first image clock signal with the passage of time, and the first image clock signal Generating means for generating a second image clock signal whose phase is adjusted with respect to the phase of
Based on the first image clock signal and the image data, a first drive signal for emitting the first light beam from the first light emitting point is generated, and the second image clock signal and Based on the image data, a second drive signal for emitting the second light beam from the second light emitting point is generated, and based on the first drive signal and the second drive signal Driving means for driving the light source;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the generation unit generates a reference clock signal, and generates the first image clock signal and the second image clock signal based on the reference clock signal. apparatus.   The generating means is configured to detect a phase of the first image clock signal based on a distance between an exposure position of the first light beam and an exposure position of the second light beam in a rotation axis direction of the photoconductor. The image forming apparatus according to claim 1, wherein the second image clock signal whose phase is adjusted is generated.   The generating means is configured to detect a relative relationship between a pixel formed by the first light beam and a pixel formed by the second light beam in a scanning direction of the first light beam and the second light beam. 3. The image forming apparatus according to claim 1, wherein the second image clock signal having a phase adjusted with respect to a phase of the first image clock signal is generated so that a shift is suppressed. .   The generating means includes an exposure start position on the photoconductor by the first light beam in the scanning direction of the first light beam and the second light beam, and on the photoconductor by the second light beam. 2. The second image clock signal whose phase is adjusted with respect to the phase of the first image clock signal so as to suppress a relative deviation from an exposure start position. Or the image forming apparatus according to 2;   Detection means for detecting the first light beam deflected by the deflection means is provided, and the generation means is based on the reference clock signal based on the timing at which the detection means detects the first light beam. The image forming apparatus according to claim 2, wherein the first image clock signal and the second image clock signal are generated.   The generation unit includes an initial frequency of the first image clock signal generated based on the reference clock signal in response to the detection of the first light beam by the detection unit, and the second image clock. The first image clock signal and the second image clock signal are generated so that the initial frequency of the signal is the same, and exposure positions of the first light beam and the second light beam in the scanning direction are generated. The image forming apparatus according to claim 6, wherein generation timings of the first image clock signal and the second image clock signal are made different according to a difference between the first image clock signal and the second image clock signal.   The image according to any one of claims 1 to 6, wherein the frequency of the first image clock signal modulated according to the passage of time and the modulation amount of the second image clock signal are the same. Forming equipment. The generation unit is an image in which the first light beam or the second light beam is emitted to form the electrostatic latent image on the photoconductor based on a detection result of the detection unit. Discriminate between the formation period and the non-image formation period that is other than that,
The generating means generates a first image clock signal and a second image clock signal whose frequencies vary with time based on the frequency of the reference clock signal in the image forming period, and the non-image The image forming apparatus according to claim 6, wherein the frequency of the first image clock signal is controlled to be constant during the formation period, and the frequency of the second image clock signal is modulated with the passage of time.   The frequency modulation period of the second image clock signal in the non-image forming period is longer than a frequency modulation period of the second image clock signal in the image forming period. Image forming apparatus. The generation unit is an image in which the first light beam or the second light beam is emitted to form the electrostatic latent image on the photoconductor based on a detection result of the detection unit. Discriminate between the formation period and the non-image formation period that is other than that,
The generating unit generates the first image clock signal and the second image clock signal that vary with time based on the reference clock signal in the image forming period, and generates the first image clock signal in the non-image forming period. The image forming apparatus according to claim 6, wherein the frequency of the first image clock signal and the frequency of the second image clock signal are controlled to be constant.   The second light emission with respect to the first light emitting point so that a pixel formed by the second light beam is adjacent to a pixel formed by the first light beam in the rotation direction of the photoconductor. The image forming apparatus according to claim 1, wherein dots are arranged.

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